Piero stepped into rallying and WRC at relatively late stage, contesting his first rally at the age of 23. He learned fast, winning italian Fiat Uno Trophy next year and expanding his activities for next year thanks to prize money he won. Step by step his career progressed and in 1991 Piero won European Championship, driving Lancia Delta.

Then Lancia terminated their official involvement with WRC and by 1993 Piero had connections with Prodrive and soon was testing Subaru Legacy, contesting his first rally with the car only little later in June 1993. From humble beginnings Prodrive got more and more interested until he was signed to do a few WRC events with the team.

Modest WRC programme was padded with Asia-Pacific championship and suddenly Piero found out that he had quite a number of rallies to contest in. After Sainz left Subaru in 1996, Piero's role was enlarged and eventually he contested almost full season alongside Colin McRae in 1998. He never quite made his name on gravel events though he was reliable if not fast driver. His single WRC win came in Monte Carlo 1997.

From Subaru Piero moved to Seat for 1999 season. Fabrizia Pons refused to accompany him, seeing the move as a step to wrong direction. Partnering with Carlo Cassina, Piero did his best at Seat but could not work miracles and was soon dropped in favour of Didier Auriol. Last real chance came with Ford, with whom Liatti did two tarmac events in 2000 to no great avail. He then did six events with Hyundai but those were, if possible, even worse that the time at Seat.